At the point where an integrated circuit (IC) device with leads/terminations is joined to a circuit board, suitable means must be provided for making satisfactory electrical and mechanical connections between the leads/terminations and the circuit board. A lead is the metal wiring protruding from the integrated circuit package which is used to create an electrical connection with the circuit board upon which the integrated circuit will be mounted. A termination is a surface that is used to create an electrical connection between any electrical or electronic elements. A connection is deemed satisfactory when it meets industry defined requirements of visual properties of wetting and filleting and furnishes a path that does not alter the intended electrical characteristics of signals that are transmitted through it. Wetting is the ability of a liquid to spread over or cover over a solid surface with which it makes contact. Filleting is a description of the volume, height, area and circumference of a joining material used to connect two surfaces. The connection must also be mechanically permanent.
These permanent connections are usually made by soldering. In soldering, two metal surfaces are united when a solder junction is formed between them. Solder is a metal or metal composition which melts at a fairly low temperature (approximately 200 C) and wets the surfaces to which it is applied in the molten state. Solder is an alloy, such as zinc and copper, or tin and lead. Upon cooling, solder forms a permanent mechanical and electrical connection between the surface of the semiconductor lead/termination and the surface of the circuit board.
Improving the mechanical connection so as to maximize the amount of solder wetting and filleting between soldered surfaces has always been desired in the art of soldering. Others have attempted to improve the soldered connection of tin/solder plating by using special bathing processes or special plating process/fixturing techniques. Our invention is directed toward a method of manufacturing leads/terminations so as to improve their solderability. Solderability is the ability of a material or surface to be wetted with molten solder under specified conditions.